Compact camera modules have become a standard component in mobile devices such as mobile phones, tablets, hand held game computers, and note books. A camera module consists of PCB board, an imaging sensor module and a lens module. The lens module consists of a lens assembly and a housing shielding it from unwanted light and environmental influences. The housing may also be shared with the housing of the complete camera module. The outer contours of a compact camera module are in many cases designed as drop-in component into mobile devices. Lens modules can also be incorporated into an illumination module, which illumination module further comprises a light source, such as a LED. Wafer level optical lens modules are consequently utilized in camera modules of cellular phones, for example.
The mass volume requirements together with the increasing drive for reducing costs triggered the development of wafer level based methods for producing and packaging the camera modules and related image sensor and optics.
The aim of packaging is to integrate the several optical, mechanical, environmental and electronic functions of a compact camera module and a lens module. For this purpose, size reduction in all directions is an important issue. This includes reduction in height (shortening van the optical path of the lens module) and in reduction of the foot print and the pitch of the components on a wafer. For instance, elimination of glass substrates contributes to lower height and costs. Foot print reduction is realized through wafer level integration light transmitting optical structures with light blocking structures such as partition walls and housings. The need for integrating partition walls originates from the fast growing market of array camera's and optical sensors.
The functional elements consist of an optical active element such as LED or VCSEL light source or a CMOS or CCD image capturing device, the imaging lenses together with optical functions such as IR filters, AR coats and light blocking structures such as baffles etc. In most cases, micro lenses and color filters are positioned on the image sensor surface.
The lens elements are usually formed by injection moulding or glass pressing. Integrated lens stacks relating to lens assemblies based on wafer level manufacturing have been disclosed in WO2004/027880. In this process, lens elements, spacers and other optical functions are manufactured at the wafer level. After singulation (i.e. separation of the wafer into individual modules) integrated lens modules are obtained.
Wafer level manufacturing of opto-electronic components in general assumes a wafer to wafer assembly of the optics wafer with the image sensor wafer. The aim is to reduce costs through maximizing the simultaneous processing of components followed by a singulation, usually dicing step. This assumption is based on the very high yields using state-of-art manufacturing front end processes for electronic components on silicon wafers. These processes benefit from a decades track record of process development using silicon as a substrate. However, the processes for manufacturing optical components on wafer level are based on different materials (glass, polymer) and processes (injection moulding, UV, thermal replication, glass pressing). In addition, refractive optical structures require extreme, i.e. high, shape accuracies with comparably high aspect ratios. So, in many cases, the yield involving manufacturing of optics on wafer level is lower than may be obtainable for electronic components. As a result an image sensor module wafer with good yield may be assembled on an optical wafer with a lower yield.
US 2013/003199 relates to a method of manufacturing a lens unit, the method comprising: preparing a preliminary lens array substrate including an opening for exposing a lens region where a lens part is formed; placing the preliminary lens array substrate at an inside of a mold; forming the lens part in the opening by injecting a resin material into the inside of the mold such that the opening is filled with the resin material and curing the resin material; and cutting the preliminary lens array substrate. The first lens unit includes a first lens part and a first support part, wherein the first lens part has a curved region having a predetermined curvature and a flat region extending in the lateral direction from the curved region. A first support part is disposed around the first lens part and the first support part has a hole in which the first lens part is installed such that the first lens part can be attached to a lateral side of the hole wherein a lateral side of the first lens part may adhere to the inner wall of the hole, especially the lateral side of the first lens part may be integrally formed with the inner wall of the hole.
US 2011/211105 relates to a lens array, comprising: a substrate in which a plurality of through holes are formed; and a plurality of lenses provided in the substrate by burying the plurality of through holes, wherein a part of the through hole is different in at least one of sectional shape and opening area of the through hole, which are taken in parallel with a surface of the substrate, from another part of the through hole in a depth direction.
US 2011/222171 relates to a method of forming an optics block, comprising: providing a substrate having first and second opposing surfaces, the substrate being a first material and having a plurality of through holes extending in the substrate between the first and second opposing surfaces; providing a second material, different than the first material, filling a portion of the through holes and extending on a portion of the first surface of the substrate outside the through holes; and replicating a first lens structure in the second material and corresponding to each of the through holes.
WO2010/050290 relates to a wafer lens manufacturing method for manufacturing a wafer lens provided with convex lens portions on a glass substrate by curing resin between a glass substrate and a resin mold in which concave cavities are formed.
US 2011/096213 relates to method for manufacturing a wafer-shaped optical apparatus with a base material substrate as a framework and a resin optical element section being molded at a hole of the base material substrate, the method comprising: a hole forming step of forming one or a plurality of holes in the base material substrate; a pressing step of putting an optical element resin and the base material substrate between optical element lower and upper metal molds formed to correspond to the hole, to mold at least the optical element section; and a resin curing step of curing the resin using heat or light. In addition this US2011096213 provides a lens module including a glass substrate as a base material (framework) with a plurality of holes formed therein, a resin lens formed to correspond to each of the plurality of holes, and a peripheral resin section made with the same resin material as the resin lens and formed on upper and lower surfaces of the glass substrate in the periphery of the resin lens. The present inventors are of the opinion that no light leakage through the bottom side is allowed when mounting the optical component on a device (e.g. LED emitter). Transparent materials and/or bubbles can cause light leakage. In addition trapped air bubbles cause poor adhesion and delamination resulting from pop corning during heat treatment. Thus light blocking must be guaranteed over the entire wall below the bottom lens surface.
US 2011/222173 relates to a method of fabricating a wafer level optical lens substrate, comprising: providing a substrate; forming at least one through hole on the substrate and forming a flange on a side wall in each through hole; and forming a lens on the flange in each through hole and embedding the lens with the flange.
US 2009/022949 relates to a process for producing a functional-element-mounted module, comprising the steps of disposing a substrate having mounted thereon a functional element having a mounting portion and a resin sealing plate formed therein with an opening corresponding in position to the functional portion of the functional element as opposed to each other at a predetermined distance; and impregnating and filling a sealing resin between the substrate and the resin sealing plate utilizing a capillary phenomenon.
In addition, when assembling a lens module upon the image sensor module, the distance between the bottom optical surface of the lens module and the image plane has to be very accurately controlled. This can be performed through active alignment assembly methods, wherein the image is projected on an image sensor and the quality of the resulting focal position is measured. According to the result, the lens module is vertically displaced to a position where an optimal image quality is obtained. The whole procedure of measuring and adjusting is time consuming and requires expensive assembly with in line focus length measurement.
From U.S. Pat. No. 3,532,038 there is known an optical system in which a transparent base member is provided with lenticular lens cavities, which cavities are filled with a refractive fluid, the surface of which fluid is covered with a cover member. The cover member is provided with an aperture plate, on which finally a second base member is present, which is also provided with lenticular lens cavities, which cavities are likewise filled with a refractive fluid.
From US 2004/0100700 there is known a method of manufacturing a micro lens array, wherein the cavities in a mould are filled with a UV curable resin, whilst the resin outside the cavities is removed by placing a transparent quartz board on top of the mould. The fluid present in the cavities is then formed into a plurality of separate lenses, whereupon a second UV curable resin layer is applied to the transparent board, which resin layer is cured by making use of the already formed separate lenses. The excess amount of the cured second resin layer is removed by using an organic solvent. Only one layer of replicated lenses is mentioned in the document, which lenses are separately arranged and do not exhibit any interconnection.
From International application WO 03/069740 in the name of the present inventor there is also known a replication process by which an optical element is formed.
WO2012/100356 relates to a method for manufacturing a plurality of optical devices, comprising the steps of: providing a replication tool, the replication tool comprising a replication surface defining an array of replication cells, each replication cell comprising a lens replication portion and a spacer replication portion, bringing the replication tool and a support in contact with each other with replication material between the replication surface and the support; causing the replication material to harden, wherein, during the step of causing the replication material to harden, the lens replication sections are caused to be kept at a distance from the support.
From the above state of the art there are thus known methods by which optical systems are obtained which are made up of separately manufactured optical elements, as a result of which the dimensions of such systems may be considered to be large. In addition, the positional accuracy, viz. in the X, Y and Z directions (between the lens surfaces) of such systems may be called critical.
The method of replicating of lenses within the apertures of a spacer wafer has an effect on the height, but still requires a tight tolerance of the stiff substrate used. In addition, the control of the shape of the lenses is somewhat difficult, especially the risk of the formation of bubbles, and/or a multistage process is required, comprising steps of, inter alia, filling holes with polymer, curing thereof, flattening of filled spacer wafer and replicating lenses on the filled holes.
Thus it is an object of the present invention to provide a method for manufacturing an optical unit in which the desired dimensional precision of the lens system can be achieved without the dimensions of the optical unit increasing undesirably.
Another object of the present invention is to provide a lens assembly, in which well defined lens shapes are present.
Thus it is an object of the present invention to provide a method for manufacturing full polymer lenses with integrated light blocking side walls.